1. Field of the Invention
The present invention relates to improved articles of footwear, particularly shoes having improved step cushioning and ventilation of the foot of the wearer. More particularly still, it relates to improvements in midsoles.
2. Background Art
A large number of sport shoes such as running shoes have been disclosed in the art and many are on the market, displaying various forms of midsole for the purpose of improving the performance of athletic shoes. Many shaped outsoles, which are the only portions which actually contact the ground, have been proposed to provide shock absorption features.
Many items of prior art are known, such as U.S. Pat. No. 4,782,603 issued Nov. 8, 1988, to S. C. Brown. This patent provides a separate molded midsole encapsulating a series of parallel, spaced-apart tubes, disposed in a generally transverse position with regard to the length of a shoe. The parallel tubes are subject to compression with the step of the wearer, and the patent states that the tubes must be of sufficient resiliency and strength to resist collapse along their walls.
U.S. Pat. No. 4,316,332 issued Feb. 23, 1982, to Giese et al shows an outsole with hollow portions adapted to retain a shock absorbing material, and surrounded by a comparatively hard rim portions of the outsole.
U.S. Pat. No. 4,608,768 issued Sep. 2, 1986, to Cavanagh discloses the use of plugs which are inserted in an openwork support forming a midsole. The plugs are made of a material that is harder than that of the midsole.
U.S. Pat. No. 4,831,749 issued May 23, 1989, to Tsai discloses a footwear including a ventilating and massaging insole having a plurality of upper beads protruding upwardly to touch a wearer's foot and a plurality of lower beads protruding downwardly to ride on a footwear sole so that upon a depression of a wearer's foot on the insole, an air flow will be pumped through holes each hole formed between each upper bead and each lower bead for ventilating the wearer's foot and for massaging the same.
U.S. Pat. No. 4,685,224 issued Aug. 11, 1987, to Anger discloses the use of a labyrinth of ventilation channels between the top-sole of a hose and the underside of the foot. This is intended to provide a pumping effect to move air around and ventilate the foot of the wearer.
U.S. Pat. No. 3,418,731 issued Dec. 31, 1968, to Anciaux discloses the use of an insole for a shoe provided with upper and lower surfaces of resilient material, and the upper surface of the sole being provided with a plurality of blind recesses, and the bottom surface being provided with corresponding projections so as to provide some ventilation during the action of walking.
The apparently closest background art encountered in the preparatory search in U.S. Pat. No. 4,845,863 issued Jul. 11, 1989, to Lin Yung-Mao which discloses the use of an insole or midsole in an active wear shoe. The specification deals with an impermeable midsole/insole construction with downwardly projecting resilient members, with those members being so placed and sized as to fit into receptables in the outsole to cushion the step of a wearer. The patent describes prior art deficiencies as follows:
Thus, conventional midsoles do not offer anything in the way of independent suspension or deformation of various areas thereof, and further are suited to only a particular weight class or cushion ability preference of wearers.
The need for a midsole having a plurality of cushioning elements, each demonstrating an individual suspension and deforming independently from the remaining elements has generally been met by the custom midsole as disclosed in U.S. Pat. No. 4,733,483, Mar. 29, 1988, to Lin. However, it has been found that a flat outsole and midsole as disclosed therein have a tendency to create a springboard effect which causes the heel to bounce and vibrate. Unless the midsole fits perfectly into the cavity created within the shoe, there is also a tendency for the midsole to slip therein. Thus, a need has arisen for a midsole that has a plurality of cushioning elements with individual suspension that does not slip or vibrate.
Related U.S. Pat. No. 4,843,741 issued Jul. 4, 1989, also to Lin Yung-Mao, discloses similar structures, but additionally the downwardly depending plugs are provided with generally cylindrical cavities in each element, for the purpose of reducing the weight of the midsole.
For further background material, the reader is directed to an article in New Scientist of 15 Jul., 1989, by Alison Turnball "A Race for a Better Running Shoe", pages 42-44, and the immediately following article "How Elastic is a Running Shoe?" by Alexander and Bennett, pages 45 and 46. The authors discussed a recent trend in athletic shoe manufacture which aims to return to the runners some of the energy expended in taking each step. Many disclosures in the prior art are directed at means for achieving some return of energy in this fashion. Alexander and Bennett sum up their test results as follows:
"The quality to look for in a shoe's heel is probably high compliance (or peak deformation), which will reduce the forces of impact. Looking at the same thing in a different way, the heel should be able to absorb the foot's kinetic energy without developing large forces, so large values in "peak deformation" and "work of deformation" are probably good. PA0 High energy return in the forepart of the sole does seem potentially important (see Table 3). But the figures from our tests for the percentage of energy returned still do not tell us how much energy a shoe returns. For that, we need to know how much energy was stored in the first place. The higher the compliance (or peak deformation) and the work of deformation, the more energy the sole stores as it is compressed. The higher the energy return, the more of that energy is recovered in the elastic recoil."